US3783170A - Electric arc furnace apparatus having a shaped magnetic field for increasing the utilized area of the arcing surface of an electrode and improving the heating efficiency - Google Patents

Electric arc furnace apparatus having a shaped magnetic field for increasing the utilized area of the arcing surface of an electrode and improving the heating efficiency Download PDF

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US3783170A
US3783170A US00291470A US3783170DA US3783170A US 3783170 A US3783170 A US 3783170A US 00291470 A US00291470 A US 00291470A US 3783170D A US3783170D A US 3783170DA US 3783170 A US3783170 A US 3783170A
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electrode
melt
magnetic field
tip
furnace
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F Kolano
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CBS Corp
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Westinghouse Electric Corp
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    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B7/00Heating by electric discharge
    • H05B7/02Details
    • H05B7/06Electrodes
    • H05B7/08Electrodes non-consumable

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  • ABSTRACT The unit heat flux to a fluid-cooled electrode and the heat flux to the material being heated by a diffused arc column operating at a given electric current level are controlled by a magnetic field coaxial with the electrode, part of the flux lines of which pass through both the arcing surface of the electrode and the molten bath.
  • the magnetic field pattern at the electrode and near the electrode is shaped into desired configurations to accomplish the purposes of the invention by the use of high permeability material in the electrode in some embodiments, and permanent magnets in the electrode in other embodiments. Where high permeability material is employed, the material may form part of the electrode tip and be substantially symmetrical around the inside and outside diameter of the tip, or may be so proportioned as to provide an outside diameter biased electrode tip.
  • the tip may be constructed of copper and high permeability material disposed within the tip either in the form of a short ring, or axially and radially extending material occupying a substantial portion of the volume of the tip and the supporting column.
  • a permanent magnet is employed, it is disposed in the tip, and the north and south poles of the permanent magnet may be axially disposed with respect to each other with their axis parallel to the axis of the electrode.
  • the poles of the permanent magnet are selectively in opposition to a field set up in the furnace by a solenoid, or selectively in polarity adding to the field set up in the furnace by the solenoid.
  • the permanent magnet may have its north and south poles lying perpendicular to the axis of the electrode.
  • the north pole of the permanent magnet may be on the side thereof adjacent the axis of the electrode, or may be on the side thereof farthest from the axis of the electrode, nearer to the wall of the furnace and nearer to the solenoid setting up a magnetic field within the furnace.
  • FIG. 1 A first figure.
  • the invention relates to an electric arc furnace having an electrode and a solenoid adjacent the wall of the furnace for setting up amagnetic field in the furnace around the electrode, within the melt, and between the electrode and the melt, and in which the electrode contains means for shaping the magnetic field of the solenoid at or near the tip of the electrode to obtain operating advantages.
  • a permanent magnet in the form of a ring with its axis extending parallel to the axis of the electrode and having the inside and outside surfaces of the ring forming the north and south magnetic poles of the magnet so that the poles lie in a direction perpendicular to the axis of the electrode is described and claimed in the copending application of S. M. DeCorso et al. for fluid cooled electrode having permanent magnets to drive the arc therefrom and apparatus employing the same, Ser. No. 4488, filed Jan. 21, 1970, the above-identified copending application being assigned to the assignee of the instant invention.
  • the relative distances between the sources of magnetic energy or the generators of magnetomotive force were such that the net electric field adjacent the electrode tip was relatively strong even though the magnetomotive force generated by the electrode tip electromagnet was relatively smaller than the magnetomotive force produced by the solenoid. This caused a relatively constrained circumference of rotation for the arc. This may be useful in a furnace startup condition where stirring is a more important function than it is at other times during a melting process such as when the melt has become hot.
  • Furnace apparatus preferably cylindrical, has an electrode mounted therein to form an arc to a melt and has a solenoid so disposed with respect to the electrode and the melt, the axis of the solenoid being parallel to and preferably substantially coinciding with the axis of the electrode, that a magnetic field is set up in the furnace with magnetic field lines extending in the furnace substantially upward beyond the positionof the arcing surface of the electrode and extending downward through the melt substantially lower than the surface of the melt, as well as through the space in the furnace lying axially therein between the arcing surface and the melt surface.
  • the electrode which may be classified in two general classes, a first class depending upon material of high permeability contained or included within the electrode to provide a low reluctance path and shape the magnetic field, or a second general class in which the electrode includes a permanent magnet to shape the total magnetic field.
  • the first class according to whether the electrode tip itself is made at least in part of high permeability material, or whether the electrode tip is made of some other material such as copper and high permeability material is included in the tip, or in the tip and/or the supporting column for the tip.
  • Certain preferred variations in the location of the high permeability material and the amount thereof give certain preferred shapings of the magnetic field set up by the solenoid to accomplish certain desired results.
  • the polarity of the permanent magnet may be such that its field opposes of adds to the solenoid field, both of said permanent magnetic in fields, said two polarity positions adding to or opposing the solenoid field giving different shaping of a total field including the solenoid field and each providing a desirable field shaping to accomplish certain objectives which are not necessarily mutually exclusive.
  • the polarity may be selected so that any particular magnetic pole lies on the side of the electrode toward the axis of the electrode and toward the axis of the solenoid field, or said last-named magnetic pole may lie on the side of the electrode away from the axis thereof and closer to the wall of the furnace and to the turns of the solenoid, both of said magnetic pole configuration providing field shapes which are different from each other, which are utilized to accomplish certain objectives and the control of the are on the arcing surface of the electrode, on the SLIXfaC Of the melt, and within the axial space between the melt and the electrode tip, said objectives not necessarily being exclusive of each other.
  • FIG. 1A illustrates the magnetic field set up by a solenoid in a furnace in the region adjacent an electrode and the region between an electrode and a melt where the electrode neither sets up a magnetic field by means contained within the electrode nor contains or includes any means for disturbing the normal field pattern set up by the solenoid;
  • FIG. 18 illustrates the magnetic field set up in a furnace by an electrode containing a permanent magnet in which the poles of the magnet are axially disposed with respect to each other in a direction corresponding to the axis of the electrode and where no solenoid field is present;
  • FIG. 2A illustrates the shaping of a solenoid field where the electrode tip is at least partially composed of high permeability material, portions of which are symmetrically locatedin the portion of the tip which has an inside diameter and the portion of the tip which has an outside diameter;
  • FIG. 28 illustrates the shaping of a solenoid field where the electrode has only a small portion of the total high permeability material adjacent the inside wall of smaller diameter and a very large portion of the high permeability material in the inside wall of the tip and/or electrode column forming the outside diameter and producing an outside-diameter-biased electrode tip;
  • FIG. 2C illustrates the shaping of a solenoid field where the electrode tip and electrode supporting column are composed of diamagnetic material, the tip being composed, for example, of copper, and there is disposed within the tip a ring relatively small thickness and of relatively small height composed of high penneability material; 7
  • FIG. 2D illustrates the shaping of a solenoid field where the electrode includes a massive volume of high permeability material having a greater radial dimension than that of FIG. 2C and having a substantially greater axial dimension than that of FIG. 2C;
  • FIG. 3A illustrates the shaping of the magnetic field where the tip and supporting column of the electrode are composed of diamagnetic material, and there is located within the tip a permanent magnet with the poles thereof axially disposed with respect to each other in a direction parallel to the axis of the tip, and the polarity of the permanent magnet is in the same direction as the polarity of the magnetic field generated by the solenoid so that in effect the magnetic fields of the solenoid and the permanent magnet add;
  • FIG.'3B shows the shaping of the magnetic field of a solenoid
  • the electrode has a tip supporting column composed of a diamagnetic material with a ringshaped permanent magnet located in the tip with its opposite poles disposed with respect to each other axially in a direction parallel to the axis of the electrode, the permanent magnet being so poled with respect to the field of the solenoid that the field of the magnet and the field of the solenoid oppose each other;
  • FIG. 4A shows the shaping of a solenoid field where the electrode tip and column are composed of diamagnetic or paramagnetic material and the electrode has a permanent ring magnet located in the tip with the inside wall of smaller diameter of the magnet forming one magnetic pole and the outside wall of larger diameter of the ring magnet forming the other magnetic pole where the north magnetic pole of the field set up by the solenoid is at the upper end of said field and the south magnetic pole of the ring magnet is on the inside of the ring magnet toward the axial center of the field generated by the solenoid; and
  • FIG. 4B shows the shaping of the solenoid field where the tip and electrode column are composed of diamagnetic or paramagnetic material, where the tip has mounted therein a ring magnet with the inside wall of smaller diameter forming one magnetic pole and the outside wall of smaller diameter forming the other magnetic pole, where the north magnetic pole of the solenoid is illustrated as being at the upper end thereof, and the north pole of the permanent ring magnet is on the side thereof towards the axis of the magnetic field generated by the solenoid.
  • FIG. 1A An electrode generally designated 10 has a supporting column shown at 11 and a tip shown at 12 which is seen to be generally annular and generally U-shaped in crosssection and to have an annular space therein extending completely around the tip, the space being designated 13.
  • the wall of the furnace is shown at 15, the solenoid winding at 16 the melt at 17 and magnetic field lines of the magnetic field set up by the solenoid at 19. It will be understood that for convenience of illustration only half of the electrodes and half of the furnace are shown, it being understood that the other half is generally symmetrical with the half shown. For the present purposes of the description of FIG. 1A, the field intensity at every point within the furnace need not be described.
  • the field intensity may be calculated according to formulas contained in many standard textbooks on Electrical Engineering, for example, a work entitled Direct and Alternating Currents by E. A. Loew, 2nd Ed., McGraw-I-Iill Co., Inc., 1938, pp. 67-72 inc. and pp. 81 and 82.
  • the tip is also shown as having a generally U-shaped passageway therein extending around the entire tip for the flow of cooling fluid to conduct heat flux from the tip, the passageway being shown at 20 and provided for reasons hereinafter to be described.
  • FIG. 1B it is assumed that the solenoid 16 is not energized or is removed, so that there is no solenoidal field present within the furnace and the only magnetic field created therein is produced by a permanent magnet 22 mounted within the electrode tip and having its magnetic poles generally axially disposed with respect to each other and producing a magnetic field having field lines 24.
  • certain of the magnetic field lines 19 extend in a substantially axial direction between the surface of the melt l7 and the electrode tip 12.
  • the effect of such magnetic field linesis to tend to focus an are between the electrode tip and the melt and to control the area of the surface of the melt on which the arc impinges.
  • Electrodes utilizing a magnetic field in the tip for this purpose are exemplified by US. Pat. No. 3,369,068 issued Feb. 13, 1968 to P. F. Kienast, and US. Pat. No. 3,385,987 issued May 28, 1968 to c. B. Wolfe et al., both of said patents being assigned to the assignee of the instant invention.
  • the magnetic field of FIG. 1B is seen to have some of the field lines extending between the arcing surface of the tip and the melt.
  • the effect of these field lines is not only to focus the are on the melt but it.has been found in. practice that if a magnetic field produced in the tip exceeds a certain strength, focusing of the arc at the tip may produce the undesirable result of concentrating the arc path over a very narrow track on the tip with the result that erosion of material from the tip is increased.
  • FIG. 2A a magnetic field is set up within the furnace having wall by solenoid 16, and in which an electrode generally designated 30 has a supporting column 31 and an annular tip 32 generally U-shaped in cross section with a space 33 therein, the tip being at least largely composed of a high permeability material indicated by the shaded material at 34.
  • the lines of the magnetic field generated by solenoid 16 are shown at 36; it is seen that there is a concentration of field intensity at the bottom as indicated by the' increase in the number of lines and the close spacing of the lines designated 36a.
  • an electrode generally designated 40 has supporting column 41 and a tip 42 with an annular space 43, and the field lines of the magnetic field generated by solenoid 16 are shown at 46.
  • the portion of the tip and supporting column composed of high permeability material is designated 44 and it is seen that the volume of high permeability material within the tip is much greater in the outsidewall portion thereof than it is in the inside wall portion thereof, and that high permeability material 44 may have a portion thereof 440 which extends axially well above the mean height of the tip and may be thought of as forming part of the supporting column.
  • FIG. 2C where an electrode generally designated 50 has a supporting column 51 with a tip 52 composed of diamagnetic material such as copper, in the annular space 53 of which there is disposed a ring of high permeability material 54.
  • the field lines of the magnetic field generated by solenoid 16 are shown at 56.
  • the radial dimension of ring 54 of high permeability material is substantially less than the radial dimension of tip 32 of FIG. 2A of high permeability material, and the magnetic field lines 56a while concentrated in the area of the furnace between the tip and the melt are shown to converge as they approach the high permeability material of the ring 54.
  • Electrode generally designated 60 has a supporting column 61 with the tip 62 having an annular space 63 therein and mounted in the electrode and extending into the space within the tip and extending a substantial distance axially within the supporting column is a large mass of high permeability material 64.
  • the field lines of the solenoid are shown at 66.
  • FIGS. 2A through 2D inclusive may best be described with reference to prior art problems which the apparatus and processes of the instant invention solve. It is well known that at low gas pressures, electrical current can pass across a gap between electrodes as a diffused discharge of several different types all of lesser intensity than that which is commonly associated with arcs. It is also well known that a portion of the discharge including the arc can be altered by the use of magnetic fields.
  • the induced motion consists of rotation of the discharge column about the common axis without a change in the area of the arcing surface of the electrode which is subjected to heat flux.
  • the arc is diffused enough, local heat flux to the electrode will be sufficiently low to prevent electrode damage.
  • an increase in the electrical current in the are or a decrease in the diameter of the diffused arc may burden the capacity of the electrode cooling system beyond its capability to remove heat flux resulting in erosion of the electrode surface by melting or vaporization.
  • my invention proposes to control, and shows a number of embodiments of apparatus for controlling, the unit flux to a cooled electrode and the material being treated by a diffused arc column operating at a given electric current level, by means of a shaped magnetic field, the field being generated by means which by itself would produce a magnetic field with the magnetic field lines coaxial with the electrode, the electrode itself including means for distorting the generated magnetic field and shaping it in a manner to facilitate operation of the furnace to prolong the life of the electrode.
  • the objects of my invention are accomplished by shaping the field and controlling the flux lines which pass through both the cooled electrode sur face and the molten bath, and further by controlling the portion of the total area of the arcing surface on which the flux lines impinge as well as controlling the portion or portions of the arcing surface on which the flux lines impinge where this is desirable to improve the operation of the apparatus.
  • An example of a magnetic field generated by a solenoid adjacent the wall of a furnace with an electrode in the furnace having an axis substantially coaxial with the axis of the solenoid is shown in FIG. 1A without any shaping or distortion of the solenoid field by means within the electrode.
  • an electrode such as shown in FIG.
  • FIG. 1A having no means to generate a field, and no means to distort a field, and operating within an area where a magnetic field is generated by a solenoid, the motion of electrified particles is unimpeded along flux lines and restricted perpendicular to them, electrified particles emanating at either the electrode or bath tend to be confined along lines of flux passing through both.
  • the general type of field shown in FIG. 1A is used to provide in vacuum metal melting furnaces stirring action in the molten pool, such for example as the apparatus shown and described in U.S. Pat. No. 3,108,151 issued Oct. 22, 1963 to Garmy et al. for Electric Furnace.”
  • the field in FIG. 1A of this patent and generally in the prior art is produced by a solenoid external to the electrode and external to the means enclosing the working volume of metal.
  • My invention resides at least in part in the discovery that an externally produced magnetic field generally coaxial with the electrode can be distorted locally by means within the electrode to change the effective electrode surface area and the melt or bath surface area intercepted by a given set of flux lines.
  • FIGS. 2A and 2B show means for distorting the magnetic field in which the electrode tip is composed of high permeability material, the tip of FIG. 2A having on the inside and outside diameter thereof amounts of high permeability material not greatly different from each other, the tip of FIG. 2B having a considerably greater amount of high permeability material on its outside surface than it does on its inside surface so that the tip of FIG. 2B is referred to herein as an outside diameter biased electrode tip.
  • a tip constructed according to the illustration of FIG. 2A gives substantially uniform arc distribution over the whole bottom surface of the tip, which bottom portion may in that case consist of, in effect, the entire arcing surface; on the other hand the tip of FIG. 2B, while increasing the flux deni sity along the bottom surface of the electrode tip, also distorts the magnetic field of the solenoid so that flux lines extending between the melt and the electrode impinge on the outside wall of larger diameter of the electrode, the last-named wall portion then becoming in some cases part of the arcing surface.
  • FIGS. 2C and 2D where shaping or distortion of the field is produced by high permeability material located within the electrode.
  • shaping of the field as shown in FIG. 2C, it is seen that as may be expected flux lines emerging from the melt tend to converge toward the ring of high permeability material 54 in the electrode and in effect there is some concentration of flux over a predetermined portion of the arcing surface of the tip.
  • the flux concentration on the tip in FIG. 2C is strongest at a radial position corresponding to the mean diameter of high permeability ring 54, and the magnetic field is weakest at any point measured on either the inside or outside surface of the tip which has an axial position corresponding to the midpoint of ring 54 taken in an axial direction. 7
  • FIG. 2D where there is not only high permeability material within the tip but a substantial volume of high permeability material is located within the electrode supporting column and extends axially upward well beyond the tip. It is seen from the magnetic field pattern of FIG. 2D that flux lines of the field extending between the melt and the electrode not only converge toward the bottom of the tip but are also caused to converge toward the outer wall of the electrode tip; the effect of the electrode tip construction shown in FIG.
  • 2D is to distribute the flux lines on a larger portion of the total area of the arcing surface of the tip, allowing that portion of the cooling fluid in the passageway in the tip to conduct heat flux from a larger portion of the total area of the arcing surface of the tip, thereby reducing the requirement for minimum heat flux removal capability.
  • FIGS. 3A and 38 where the magnetic field of the solenoid is distorted by a permenent magnet located within the tip of the electrode.
  • the magnetic fields of the solenoid and the permanent magnet within the tip are of such a polarity that they add to each other with the result that there is an increase in flux lines converging on the arcing surface of the electrode adjacent the permanent magnet.
  • the field generated by the permanent magnet in the tip is of such a polarity that it opposes the magnetic field generated by the solenoid.
  • the field configuration of FlG. 3B tends to bring the are up the core or center of the electrode. It will be noted that in the area generally designated X in the drawing the flux is substantially zero and there could be an arc path between the melt and the electrode passing through the area designated X.
  • FIGS. 4A and 4B In the electrode illustrated in both of these figures a permanent magnet is located within the electrode tip, the permanent magnet consisting of a ring with a generally axially extending inner wall of smaller diameter and a generally axially extending outer wall of larger diameter and the magnetic poles of the permanent magnet in both cases are on the inside and outside walls of the permanent magnet.
  • the field illustrated in FIG. 4A generated by the solenoid has a north to south polarity in which the north pole lies at the upper end of the field illustrated, while the south pole lies at the lower end portion of the field illustrated, and the permanent magnet within the tip has its south magnetic pole formed by the inside surface of smaller diameter and its north magnetic pole formed by the outside surface of larger diameter.
  • the magnetic field configuration shown in FIG. 4A tends to concentrate the arc and consequently the heat generated by the are spot on the bottom or face and on the inside diameter or inside surface of the electrode tip.
  • the field of the solenoid has a similar polarity to that shown in FIG. 4A, but the polarity of the permanent magnet within the tip is reversed and in FIG. 4B the outside surface of larger diameter constitutes the south magnetic pole of the permanent magnet while the inside surface of smaller diameter forms the north magnetic pole of the permanent magnet.
  • the resultant magnetic field tends to concentrate flux lines on the face or bottom and on the outside diameter of the electrode tip with a resulting effect that the are tends to occur predominately from these "portions of the arcing surface and most of the heat flux removal by cooling fluid in the tip from these portions of the arcing surface of the electrode.
  • the various embodiments of my invention provide great versatility in determining the portion of the total area of the arcing surface upon which the arc can be expected to impinge and also provide great versatility in limiting the arc to a certain desired portion of the arcing surface, or in utilizing certain' desired portions of the arcing surface of the tip to utilize the maximum heat flux transfer capabilities of the electrode, to concentrate the are on the melt within the furnace in accordance with flux lines extending between the electrode and the melt, to stir the melt, and to prevent undesirable modes of operation of the are from the electrode.
  • Indicated positions of permanent magnets and ferromagnetic parts within the electrode envelope should not be interpreted to mean that these elements are permanently fixed in position. Where advantageous for specific conditions during a portion of a melting cycle, these elements could be hydraulically or mechanically moved within the confines of the electrode envelope to provide a variable flux condition for a fixed arcing distance between electrode tip and melt.
  • Furnace apparatus including a furnace having a wall, said furnace adapted to contain at least partially electrically conductive material to be melted, an electrode including means forming an arcing surface mounted in the furnace in a position therein substantially perpendicular to the surface of the melt, electrical circuit means connected to the electrode and to the melt for producing and sustaining an arc therebetween, the are extending substantially parallel to the longitudinal axis of the electrode, material having a high permeability mounted in the electrode near the arcing surface, and means near the wall of the furnace for setting up a magnetic field having a component in the furnace substantially parallel to the axis of the electrode and perpendicular to the surface of the melt, said high permeability material attracting lines of force of said magneticfield and causing a concentrated field at the arcing surface extending'between the arcing surface and the melt, said concentrated field focusing the are between the electrode and the melt thereby preventing flaring of the arc toward the inside wall of the furnace.
  • Furnace apparatus adapted to have a melt of at least partially electrically conductive material, comprising an electrode electric circuit means connected to the electrode and the melt for producing and sustaining an arc therebetween, means near the furnace wall for generating a magnetic field having a component extending between the melt and the electrode, means in the electrode effective without requiring energizing power for increasing the strength of the component of the magnetic field to thereby focus the are.
  • Furnace apparatus comprising means for containing a melt which is at least partially electrically conductive, an electrode disposed in predetermined spaced relationship with the melt, the electrode and the melt being adapted to be connected to terminals of opposite polarity of a source of potential to produce and sustain an are between the electrode and the melt, means disposed close to the wall of the containing means for generating a magnetic field within the containing means and adjacent at least a portion of the electrode which extends axially between the electrode and the melt, the electrode including means effective without requiring energizing power for causing at least some of the magnetic field lines to depart in a desired manner from paths which they would normally tend to follow.
  • Apparatus according to claim 3 in which the electrode has means forming an arcing surface and in which the means for causing at least some of the magnetic field lines to depart from their normal paths is utilized for controlling the percentage of the total area of the arcing surface upon which said are impinges.
  • Apparatus according to claim 3 in which the electrode includes means forming an arcing surface and in which the means within the electrode for causing at least some of the magnetic field lines to depart from their normal paths is utilized to concentrate magnetic field lines in such a manner that an increased number enter or pass through said arcing surface than would so do were said latter means not present in said electrode.
  • Furnace apparatus comprising means for containing a melt which is at least partially electrically conductive, an electrode disposed in predetermined spaced relationship with the melt, the electrode and the melt being adapted to be connected to terminals of opposite polarity of a source of potential to produce and sustain an are between the electrode and the melt, means disposed close to the wall of the containing means for generating a magnetic field within the containing means and adjacent at least a portion of the electrode which extends axially between the electrode and the melt, the electrode including means effective without requiring energizing power for causing at least some of the magnetic field lines to depart in a desired manner from paths which they would normally tend to follow, the electrode being additionally characterized as having a tip forming an arcing surface, the tip being generally annular in a horizontal plane and generally U-shaped in vertical plane cross section along any radius with a space therein extending around the entire tip, said means for causing at least some of the magnetic field lines to depart from their normal paths disposed within the space and composed of high permeability material.
  • Furnace apparatus comprising means for containing a melt which is at least partially electrically conductivc, an electrode disposed in predetermined spaced relationship with the melt, the electrode and the melt being adapted to be connected to terminals of opposite polarity of a source of potential to produce and sustain an are between the electrode and the melt, means disposed close to the wall of the containing means for generating a magnetic field within the containing means and adjacent at least a portion of the electrode which extends axially between the electrode and the melt, the electrode including means effective without requiring energizing power for causing at least some of the magnetic field lines to depart in a desired manner from paths which they would normally tend to follow, the electrode being additionally characterized as including a supporting column with a tip, the supporting column including means forming a generally cylindrical space of at least a predetermined width, and the means for causing at least some of the magnetic field lines to depart from their normal paths is generally annular and disposed within the space and composed of high permeability material.
  • Furnace apparatus comprising means for containing a melt which is at least partially electrically conductive, an electrode disposed in predetermined spaced re-- lationship with the melt, the electrode and the melt being adapted to be connected to terminals of opposite polarity of a source of potential to produce and sustain an are between the electrode and the melt, means disposed close to the wall of the containing means for generating a magnetic field within the containing means and adjacent at least a portion of the electrode which extends axially between the electrode and the melt, the electrode including means effective without requiring energizing power for causing at least some of the magnetic field lines to depart in a desired manner from paths which they would normally tend to follow, the electrode being additionally characterized as including a supporting column with a tip, the tip having a space therein extending around the tip, the column having means fonning a generally cylindrical space of at least a predetermined width, the space in the tip being radially aligned with the space in the column, the spaces opening into each other, the means for causing at least
  • Apparatus according to claim 8 in which the high permeability material occupies both the space within the tip and at least a portion of the space within the column.
  • Furnace apparatus adapted to have a melt of at least partially electrically conductive material, comprising an electrode spaced from said melt, electric circuit means connected to the electrode and the melt for producing and sustaining an arc therebetween, at least one element for generating a magnetic field, at least one other element as part of the electrode being effective without requiring energizing power, the first and second elements cooperating with each other to produce a resultant magnetic field pattern which is shaped and dimensioned to control at least one of the operating parameters of the furnace apparatus including the total area on the electrode surface from which the arc takes place, the particular portion of the electrode surface from which the arc takes place, the total area of the surface of the melt upon which the arc impinges, the particular portion of the surface of the melt upon which the arc impinges.

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Abstract

The unit heat flux to a fluid-cooled electrode and the heat flux to the material being heated by a diffused arc column operating at a given electric current level are controlled by a magnetic field coaxial with the electrode, part of the flux lines of which pass through both the arcing surface of the electrode and the molten bath. The magnetic field pattern at the electrode and near the electrode is shaped into desired configurations to accomplish the purposes of the invention by the use of high permeability material in the electrode in some embodiments, and permanent magnets in the electrode in other embodiments. Where high permeability material is employed, the material may form part of the electrode tip and be substantially symmetrical around the inside and outside diameter of the tip, or may be so proportioned as to provide an outside diameter biased electrode tip. The tip may be constructed of copper and high permeability material disposed within the tip either in the form of a short ring, or axially and radially extending material occupying a substantial portion of the volume of the tip and the supporting column. Where a permanent magnet is employed, it is disposed in the tip, and the north and south poles of the permanent magnet may be axially disposed with respect to each other with their axis parallel to the axis of the electrode. The poles of the permanent magnet are selectively in opposition to a field set up in the furnace by a solenoid, or selectively in polarity adding to the field set up in the furnace by the solenoid. Additionally, the permanent magnet may have its north and south poles lying perpendicular to the axis of the electrode. Selectively, the north pole of the permanent magnet may be on the side thereof adjacent the axis of the electrode, or may be on the side thereof farthest from the axis of the electrode, nearer to the wall of the furnace and nearer to the solenoid setting up a magnetic field within the furnace.

Description

United States Patent [191 Kolano [451 Jan. 1,1974
[ 1 ELECTRIC ARC FURNACE APPARATUS HAVING A SHAPED MAGNETIC FIELD FOR INCREASING THE UTILIZED AREA OF THE ARCING SURFACE OF AN ELECTRODE AND IMPROVING THE HEATING EFFICIENCY Frank J. Kolano, North Braddock, Pa.
[73] Assignee: Westinghouse Electric Corporation,
Pittsburgh, Pa.
22 Filed: Sept. 22, 1972 211 Appl. No.: 291,470
[75] Inventor:
Primary Examiner-Roy N. Envall, Jr. Attorney-A. T. Stratton et al.
[57] ABSTRACT The unit heat flux to a fluid-cooled electrode and the heat flux to the material being heated by a diffused arc column operating at a given electric current level are controlled by a magnetic field coaxial with the electrode, part of the flux lines of which pass through both the arcing surface of the electrode and the molten bath. The magnetic field pattern at the electrode and near the electrode is shaped into desired configurations to accomplish the purposes of the invention by the use of high permeability material in the electrode in some embodiments, and permanent magnets in the electrode in other embodiments. Where high permeability material is employed, the material may form part of the electrode tip and be substantially symmetrical around the inside and outside diameter of the tip, or may be so proportioned as to provide an outside diameter biased electrode tip. The tip may be constructed of copper and high permeability material disposed within the tip either in the form of a short ring, or axially and radially extending material occupying a substantial portion of the volume of the tip and the supporting column. Where a permanent magnet is employed, it is disposed in the tip, and the north and south poles of the permanent magnet may be axially disposed with respect to each other with their axis parallel to the axis of the electrode. The poles of the permanent magnet are selectively in opposition to a field set up in the furnace by a solenoid, or selectively in polarity adding to the field set up in the furnace by the solenoid. Additionally, the permanent magnet may have its north and south poles lying perpendicular to the axis of the electrode. Selectively, the north pole of the permanent magnet may be on the side thereof adjacent the axis of the electrode, or may be on the side thereof farthest from the axis of the electrode, nearer to the wall of the furnace and nearer to the solenoid setting up a magnetic field within the furnace.
10 Claims, 10 Drawing Figures LJJ llllll' lllll [I PATENTEDJAN H974 SHEEI 10F 3 FIG. 18.
FIG.
PRIOR ART PRIOR ART ELECTRIC ARC FURNACE APPARATUS HAVING A SHAPED MAGNETIC FIELD FOR INCREASING THE UTILIZED AREA OF THE ARCING SURFACE OF AN ELECTRODE AND IMPROVING THE HEATING EFFICIENCY CROSS REFERECNE TO RELATED APPLICATION Certain inventions related tothose disclosed in the present application are disclosed and claimed in copending application, Ser. No. 291,433, filed concurrently by Ronald R. Akers, and assigned to the same assignee as the present application.
FIELD OF THE INVENTION The invention relates to an electric arc furnace having an electrode and a solenoid adjacent the wall of the furnace for setting up amagnetic field in the furnace around the electrode, within the melt, and between the electrode and the melt, and in which the electrode contains means for shaping the magnetic field of the solenoid at or near the tip of the electrode to obtain operating advantages.
- DESCRIPTION OF THE PRIOR ART It is old in the art to employ high permeability mate- 'rial in an electrode to provide a low reluctance path for lines of a magnetic field. Sucha general arrangement is described and claimed in US. Pat. No. 3,395,239, issued July 30, 1968 to A. M. Bruning et al for Arc Furnace Electrode and Magnetic Circuit Forming Structure for Use Therein, assigned to the assignee of the instant invention.
It is old in the art to employ permanent magnets located in an electrode for setting up a magnetic field adjacent the arcing surface thereof to exert a force on the arc and cause the arc to move around the arcing surface. A permanent magnet in the form of a ring with its axis extending parallel to the axis of the electrode and having the inside and outside surfaces of the ring forming the north and south magnetic poles of the magnet so that the poles lie in a direction perpendicular to the axis of the electrode is described and claimed in the copending application of S. M. DeCorso et al. for fluid cooled electrode having permanent magnets to drive the arc therefrom and apparatus employing the same, Ser. No. 4488, filed Jan. 21, 1970, the above-identified copending application being assigned to the assignee of the instant invention.
Suggestions as to the use of a permanent magnet in an electrode also occur elsewhere in the patented prior art. In the past a form of furnace in which two electro magnetic field producing means are used to control an arc has been, used. The specific form used comprises a furnace including a relatively short electrode tip electromagnet having 3,200 ampere turns of energizing force available and an external solenoid having 5,040 ampere turns of bucking or opposing magnetic force available. The magnetic forces involved were specifically arranged to cancel at the centerline of the electric arc furnace in which this apparatus was being used. The relative distances between the sources of magnetic energy or the generators of magnetomotive force were such that the net electric field adjacent the electrode tip was relatively strong even though the magnetomotive force generated by the electrode tip electromagnet was relatively smaller than the magnetomotive force produced by the solenoid. This caused a relatively constrained circumference of rotation for the arc. This may be useful in a furnace startup condition where stirring is a more important function than it is at other times during a melting process such as when the melt has become hot.
I SUMMARY OF THE INVENTION Furnace apparatus, preferably cylindrical, has an electrode mounted therein to form an arc to a melt and has a solenoid so disposed with respect to the electrode and the melt, the axis of the solenoid being parallel to and preferably substantially coinciding with the axis of the electrode, that a magnetic field is set up in the furnace with magnetic field lines extending in the furnace substantially upward beyond the positionof the arcing surface of the electrode and extending downward through the melt substantially lower than the surface of the melt, as well as through the space in the furnace lying axially therein between the arcing surface and the melt surface. There are several embodiments of the electrode which may be classified in two general classes, a first class depending upon material of high permeability contained or included within the electrode to provide a low reluctance path and shape the magnetic field, or a second general class in which the electrode includes a permanent magnet to shape the total magnetic field. There are several embodiments in the first class, according to whether the electrode tip itself is made at least in part of high permeability material, or whether the electrode tip is made of some other material such as copper and high permeability material is included in the tip, or in the tip and/or the supporting column for the tip. Certain preferred variations in the location of the high permeability material and the amount thereof give certain preferred shapings of the magnetic field set up by the solenoid to accomplish certain desired results. In the second general class there are further subclasses depending upon whether the permanent magnet has its magnetic poles axially disposed in a direction parallel to the axis of the electrode or whether the permanent magnetic has its opposite magnetic poles disposed in a direction generally perpendicular to the axis of the electrode. Where the poles are axially disposed in a direction parallel to the axis of the electrode, the polarity of the permanent magnet may be such that its field opposes of adds to the solenoid field, both of said permanent magnetic in fields, said two polarity positions adding to or opposing the solenoid field giving different shaping of a total field including the solenoid field and each providing a desirable field shaping to accomplish certain objectives which are not necessarily mutually exclusive. While the permenent magnet in the tip in the form of a ring with the outside surface of the ring of larger diameter forming one magnetic pole and the inside surface of smaller diameter of the ring formingthe other magnetic pole, the polarity may be selected so that any particular magnetic pole lies on the side of the electrode toward the axis of the electrode and toward the axis of the solenoid field, or said last-named magnetic pole may lie on the side of the electrode away from the axis thereof and closer to the wall of the furnace and to the turns of the solenoid, both of said magnetic pole configuration providing field shapes which are different from each other, which are utilized to accomplish certain objectives and the control of the are on the arcing surface of the electrode, on the SLIXfaC Of the melt, and within the axial space between the melt and the electrode tip, said objectives not necessarily being exclusive of each other.
BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention reference may be had to the preferred embodiment exemplary of the invention shown in the accompanying drawings in which:
FIG. 1A illustrates the magnetic field set up by a solenoid in a furnace in the region adjacent an electrode and the region between an electrode and a melt where the electrode neither sets up a magnetic field by means contained within the electrode nor contains or includes any means for disturbing the normal field pattern set up by the solenoid;
FIG. 18 illustrates the magnetic field set up in a furnace by an electrode containing a permanent magnet in which the poles of the magnet are axially disposed with respect to each other in a direction corresponding to the axis of the electrode and where no solenoid field is present;
FIG. 2A illustrates the shaping of a solenoid field where the electrode tip is at least partially composed of high permeability material, portions of which are symmetrically locatedin the portion of the tip which has an inside diameter and the portion of the tip which has an outside diameter;
FIG. 28 illustrates the shaping of a solenoid field where the electrode has only a small portion of the total high permeability material adjacent the inside wall of smaller diameter and a very large portion of the high permeability material in the inside wall of the tip and/or electrode column forming the outside diameter and producing an outside-diameter-biased electrode tip;
FIG. 2C illustrates the shaping of a solenoid field where the electrode tip and electrode supporting column are composed of diamagnetic material, the tip being composed, for example, of copper, and there is disposed within the tip a ring relatively small thickness and of relatively small height composed of high penneability material; 7
FIG. 2D illustrates the shaping of a solenoid field where the electrode includes a massive volume of high permeability material having a greater radial dimension than that of FIG. 2C and having a substantially greater axial dimension than that of FIG. 2C;
FIG. 3A illustrates the shaping of the magnetic field where the tip and supporting column of the electrode are composed of diamagnetic material, and there is located within the tip a permanent magnet with the poles thereof axially disposed with respect to each other in a direction parallel to the axis of the tip, and the polarity of the permanent magnet is in the same direction as the polarity of the magnetic field generated by the solenoid so that in effect the magnetic fields of the solenoid and the permanent magnet add;
FIG.'3B shows the shaping of the magnetic field of a solenoid where the electrode has a tip supporting column composed of a diamagnetic material with a ringshaped permanent magnet located in the tip with its opposite poles disposed with respect to each other axially in a direction parallel to the axis of the electrode, the permanent magnet being so poled with respect to the field of the solenoid that the field of the magnet and the field of the solenoid oppose each other;
FIG. 4A shows the shaping of a solenoid field where the electrode tip and column are composed of diamagnetic or paramagnetic material and the electrode has a permanent ring magnet located in the tip with the inside wall of smaller diameter of the magnet forming one magnetic pole and the outside wall of larger diameter of the ring magnet forming the other magnetic pole where the north magnetic pole of the field set up by the solenoid is at the upper end of said field and the south magnetic pole of the ring magnet is on the inside of the ring magnet toward the axial center of the field generated by the solenoid; and
FIG. 4B shows the shaping of the solenoid field where the tip and electrode column are composed of diamagnetic or paramagnetic material, where the tip has mounted therein a ring magnet with the inside wall of smaller diameter forming one magnetic pole and the outside wall of smaller diameter forming the other magnetic pole, where the north magnetic pole of the solenoid is illustrated as being at the upper end thereof, and the north pole of the permanent ring magnet is on the side thereof towards the axis of the magnetic field generated by the solenoid.
DESCRIPTION OF PREFERRED EMBODIMENTS Particular reference is made to FIG. 1A. An electrode generally designated 10 has a supporting column shown at 11 and a tip shown at 12 which is seen to be generally annular and generally U-shaped in crosssection and to have an annular space therein extending completely around the tip, the space being designated 13. The wall of the furnace is shown at 15, the solenoid winding at 16 the melt at 17 and magnetic field lines of the magnetic field set up by the solenoid at 19. It will be understood that for convenience of illustration only half of the electrodes and half of the furnace are shown, it being understood that the other half is generally symmetrical with the half shown. For the present purposes of the description of FIG. 1A, the field intensity at every point within the furnace need not be described. The field intensity may be calculated according to formulas contained in many standard textbooks on Electrical Engineering, for example, a work entitled Direct and Alternating Currents by E. A. Loew, 2nd Ed., McGraw-I-Iill Co., Inc., 1938, pp. 67-72 inc. and pp. 81 and 82.
The tip is also shown as having a generally U-shaped passageway therein extending around the entire tip for the flow of cooling fluid to conduct heat flux from the tip, the passageway being shown at 20 and provided for reasons hereinafter to be described.
Particular reference is made to FIG. 1B in which it is assumed that the solenoid 16 is not energized or is removed, so that there is no solenoidal field present within the furnace and the only magnetic field created therein is produced by a permanent magnet 22 mounted within the electrode tip and having its magnetic poles generally axially disposed with respect to each other and producing a magnetic field having field lines 24.
It is to be noted in connection with FIG. 1A that certain of the magnetic field lines 19 extend in a substantially axial direction between the surface of the melt l7 and the electrode tip 12. The effect of such magnetic field linesis to tend to focus an are between the electrode tip and the melt and to control the area of the surface of the melt on which the arc impinges. Somewhat similar use of a magnetic field is old in the art as exemplified for example by U.S. Pat. No. 2,978,525 to H.
Gruber et al., issued Apr. 4, 1961 for Magnetic Field Coil for Concentrating the Arc in a Vacuum Arc Furnace. The prior art also shows a magnetic field coil around a furnace to enhance stirring of the melt.
With respect to FIG. IE, it is old in the art to have means disposed in an electrode tip for producing a magnetic field having a strong field component transverse to at least large portions of the arcing surface of the electrode tip for exerting a force on an arc extending axially from the tip to cause the arc to move substantially continuously around the tip. Electrodes utilizing a magnetic field in the tip for this purpose are exemplified by US. Pat. No. 3,369,068 issued Feb. 13, 1968 to P. F. Kienast, and US. Pat. No. 3,385,987 issued May 28, 1968 to c. B. Wolfe et al., both of said patents being assigned to the assignee of the instant invention.
Generally speaking the rotating or are moving effect of the magnetic fields described in the afore-identified patents is similar to the rotating effect of the magnetic field of magnet 22 in which the magnetic poles are axially disposed with respect to each other.
The magnetic field of FIG. 1B is seen to have some of the field lines extending between the arcing surface of the tip and the melt. The effect of these field lines is not only to focus the are on the melt but it.has been found in. practice that if a magnetic field produced in the tip exceeds a certain strength, focusing of the arc at the tip may produce the undesirable result of concentrating the arc path over a very narrow track on the tip with the result that erosion of material from the tip is increased.
Particular reference is made now to FIG. 2A in which a magnetic field is set up within the furnace having wall by solenoid 16, and in which an electrode generally designated 30 has a supporting column 31 and an annular tip 32 generally U-shaped in cross section with a space 33 therein, the tip being at least largely composed of a high permeability material indicated by the shaded material at 34. The lines of the magnetic field generated by solenoid 16 are shown at 36; it is seen that there is a concentration of field intensity at the bottom as indicated by the' increase in the number of lines and the close spacing of the lines designated 36a. The advantages of a magnetic field configuration such as that' shown in FIG. 2A and its aficct upon arc operation and furnace operation will be fully described hereinafter when the various field patterns of all of FIGS. 2A, 2B, 2C, and 2D, are stated and explained fully with respect to each other.
Particular reference is made now to FIG. 28; an electrode generally designated 40 has supporting column 41 and a tip 42 with an annular space 43, and the field lines of the magnetic field generated by solenoid 16 are shown at 46. The portion of the tip and supporting column composed of high permeability material is designated 44 and it is seen that the volume of high permeability material within the tip is much greater in the outsidewall portion thereof than it is in the inside wall portion thereof, and that high permeability material 44 may have a portion thereof 440 which extends axially well above the mean height of the tip and may be thought of as forming part of the supporting column. It is noted that there is a high concentration of magnetic field strength between the tip and the melt, as indicated by lines 46a, and that also magnetic field lines indicated by lines 46b may enter the tip on the outside surface thereof and other magnetic field lines indicated by line 460 may extend from the melt to the inner wall of the arcing surface of the tip. Particular reference is made now to FIG. 2C where an electrode generally designated 50 has a supporting column 51 with a tip 52 composed of diamagnetic material such as copper, in the annular space 53 of which there is disposed a ring of high permeability material 54. The field lines of the magnetic field generated by solenoid 16 are shown at 56. It is to be noted that the radial dimension of ring 54 of high permeability material is substantially less than the radial dimension of tip 32 of FIG. 2A of high permeability material, and the magnetic field lines 56a while concentrated in the area of the furnace between the tip and the melt are shown to converge as they approach the high permeability material of the ring 54.
Particular reference is made now to FIG. 2D. Electrode generally designated 60 has a supporting column 61 with the tip 62 having an annular space 63 therein and mounted in the electrode and extending into the space within the tip and extending a substantial distance axially within the supporting column is a large mass of high permeability material 64. The field lines of the solenoid are shown at 66. There is a substantial increase in magnetic field strength between the tip and the melt as indicated by theincreased field lines 660 which converge towards each other as they approach the lower end of the massive high permeability material 64. There is an increase in magnetic field strength at the side of the tip as indicated by magnetic field lines 66b which converge towards the massive high permeability material 64. In addition there is a substantial bending or pulling of other lines of the solenoid field toward the mass of high permeability material as indicated by lines 660.
The uses and advantages of the various field configurations shown in FIGS. 2A through 2D inclusive may best be described with reference to prior art problems which the apparatus and processes of the instant invention solve. It is well known that at low gas pressures, electrical current can pass across a gap between electrodes as a diffused discharge of several different types all of lesser intensity than that which is commonly associated with arcs. It is also well known that a portion of the discharge including the arc can be altered by the use of magnetic fields.
It has been found in tests with high speed motion picture studies of current fiow between an electrode such as that described and claimed in US. Pat. No. 3,368,018 issued Feb. 6, 19.68 to S. M. DeCorso et al. for Electrode and Tip" and assigned to the assignee of the instant invention, and a molten metal pool in a vacuum melting furnace equiped with an external solenoid that the electric discharge consisted of a large diameter diffused column. This column extended across the diameter of the molten pool at its lower end and across a substantial part of the electrode base at its upper end roughly centered on the electrode axis. The edge of the column was curved in such a manner as to suggest that it conformed to flux lines of the combined magnetic field generated by field coil in the electrode and the furnace solenoid.
In the operation of such an electrode without a furnace solenoid at atmospheric pressures, an intensely hot concentrated arc is moved rapidly over the electrode surface by its interaction with the components of a magnetic field parallel to the electrodes surface. This motion distributes the heat flux from the arc route to the electrodes over a large area to prevent local overheating and consequent electrode damage. The normal magnetic field relation of a field generated by a coil in the electrode to the arcing surface of the electrode is shown in FIG. 1B illustrating the prior art.
For a large diameter diffused are which is generally coaxial with the electrode axis and the type of magnetic field generated by a field coil in the electrode, as described, the induced motion consists of rotation of the discharge column about the common axis without a change in the area of the arcing surface of the electrode which is subjected to heat flux. As long as the arc is diffused enough, local heat flux to the electrode will be sufficiently low to prevent electrode damage. However, an increase in the electrical current in the are or a decrease in the diameter of the diffused arc may burden the capacity of the electrode cooling system beyond its capability to remove heat flux resulting in erosion of the electrode surface by melting or vaporization.
As previously stated, my invention proposes to control, and shows a number of embodiments of apparatus for controlling, the unit flux to a cooled electrode and the material being treated by a diffused arc column operating at a given electric current level, by means of a shaped magnetic field, the field being generated by means which by itself would produce a magnetic field with the magnetic field lines coaxial with the electrode, the electrode itself including means for distorting the generated magnetic field and shaping it in a manner to facilitate operation of the furnace to prolong the life of the electrode. The objects of my invention are accomplished by shaping the field and controlling the flux lines which pass through both the cooled electrode sur face and the molten bath, and further by controlling the portion of the total area of the arcing surface on which the flux lines impinge as well as controlling the portion or portions of the arcing surface on which the flux lines impinge where this is desirable to improve the operation of the apparatus. An example of a magnetic field generated by a solenoid adjacent the wall of a furnace with an electrode in the furnace having an axis substantially coaxial with the axis of the solenoid is shown in FIG. 1A without any shaping or distortion of the solenoid field by means within the electrode. In an electrode such as shown in FIG. 1A having no means to generate a field, and no means to distort a field, and operating within an area where a magnetic field is generated by a solenoid, the motion of electrified particles is unimpeded along flux lines and restricted perpendicular to them, electrified particles emanating at either the electrode or bath tend to be confined along lines of flux passing through both. The general type of field shown in FIG. 1A is used to provide in vacuum metal melting furnaces stirring action in the molten pool, such for example as the apparatus shown and described in U.S. Pat. No. 3,108,151 issued Oct. 22, 1963 to Garmy et al. for Electric Furnace." The field in FIG. 1A of this patent and generally in the prior art is produced by a solenoid external to the electrode and external to the means enclosing the working volume of metal.
My invention resides at least in part in the discovery that an externally produced magnetic field generally coaxial with the electrode can be distorted locally by means within the electrode to change the effective electrode surface area and the melt or bath surface area intercepted by a given set of flux lines.
FIGS. 2A and 2B show means for distorting the magnetic field in which the electrode tip is composed of high permeability material, the tip of FIG. 2A having on the inside and outside diameter thereof amounts of high permeability material not greatly different from each other, the tip of FIG. 2B having a considerably greater amount of high permeability material on its outside surface than it does on its inside surface so that the tip of FIG. 2B is referred to herein as an outside diameter biased electrode tip.
As seen from the Figures, a tip constructed according to the illustration of FIG. 2A gives substantially uniform arc distribution over the whole bottom surface of the tip, which bottom portion may in that case consist of, in effect, the entire arcing surface; on the other hand the tip of FIG. 2B, while increasing the flux deni sity along the bottom surface of the electrode tip, also distorts the magnetic field of the solenoid so that flux lines extending between the melt and the electrode impinge on the outside wall of larger diameter of the electrode, the last-named wall portion then becoming in some cases part of the arcing surface.
Particular reference is made to FIGS. 2C and 2D where shaping or distortion of the field is produced by high permeability material located within the electrode. With reference to shaping of the field as shown in FIG. 2C, it is seen that as may be expected flux lines emerging from the melt tend to converge toward the ring of high permeability material 54 in the electrode and in effect there is some concentration of flux over a predetermined portion of the arcing surface of the tip. The flux concentration on the tip in FIG. 2C is strongest at a radial position corresponding to the mean diameter of high permeability ring 54, and the magnetic field is weakest at any point measured on either the inside or outside surface of the tip which has an axial position corresponding to the midpoint of ring 54 taken in an axial direction. 7
Particular reference is made to FIG. 2D where there is not only high permeability material within the tip but a substantial volume of high permeability material is located within the electrode supporting column and extends axially upward well beyond the tip. It is seen from the magnetic field pattern of FIG. 2D that flux lines of the field extending between the melt and the electrode not only converge toward the bottom of the tip but are also caused to converge toward the outer wall of the electrode tip; the effect of the electrode tip construction shown in FIG. 2D is to distribute the flux lines on a larger portion of the total area of the arcing surface of the tip, allowing that portion of the cooling fluid in the passageway in the tip to conduct heat flux from a larger portion of the total area of the arcing surface of the tip, thereby reducing the requirement for minimum heat flux removal capability.
Particularreference is made now to FIGS. 3A and 38 where the magnetic field of the solenoid is distorted by a permenent magnet located within the tip of the electrode. In FIG. 3A the magnetic fields of the solenoid and the permanent magnet within the tip are of such a polarity that they add to each other with the result that there is an increase in flux lines converging on the arcing surface of the electrode adjacent the permanent magnet.
In FIG. 3B the field generated by the permanent magnet in the tip is of such a polarity that it opposes the magnetic field generated by the solenoid. The field configuration of FlG. 3B tends to bring the are up the core or center of the electrode. It will be noted that in the area generally designated X in the drawing the flux is substantially zero and there could be an arc path between the melt and the electrode passing through the area designated X.
Particular reference is made to FIGS. 4A and 4B. In the electrode illustrated in both of these figures a permanent magnet is located within the electrode tip, the permanent magnet consisting of a ring with a generally axially extending inner wall of smaller diameter and a generally axially extending outer wall of larger diameter and the magnetic poles of the permanent magnet in both cases are on the inside and outside walls of the permanent magnet. The field illustrated in FIG. 4A generated by the solenoid has a north to south polarity in which the north pole lies at the upper end of the field illustrated, while the south pole lies at the lower end portion of the field illustrated, and the permanent magnet within the tip has its south magnetic pole formed by the inside surface of smaller diameter and its north magnetic pole formed by the outside surface of larger diameter. The magnetic field configuration shown in FIG. 4A tends to concentrate the arc and consequently the heat generated by the are spot on the bottom or face and on the inside diameter or inside surface of the electrode tip.
In the figure illustrated in FIG. 4B the field of the solenoid has a similar polarity to that shown in FIG. 4A, but the polarity of the permanent magnet within the tip is reversed and in FIG. 4B the outside surface of larger diameter constitutes the south magnetic pole of the permanent magnet while the inside surface of smaller diameter forms the north magnetic pole of the permanent magnet. It is seen from FIG. 48 that the resultant magnetic field tends to concentrate flux lines on the face or bottom and on the outside diameter of the electrode tip with a resulting effect that the are tends to occur predominately from these "portions of the arcing surface and most of the heat flux removal by cooling fluid in the tip from these portions of the arcing surface of the electrode.
It is seen then that the various embodiments of my invention provide great versatility in determining the portion of the total area of the arcing surface upon which the arc can be expected to impinge and also provide great versatility in limiting the arc to a certain desired portion of the arcing surface, or in utilizing certain' desired portions of the arcing surface of the tip to utilize the maximum heat flux transfer capabilities of the electrode, to concentrate the are on the melt within the furnace in accordance with flux lines extending between the electrode and the melt, to stir the melt, and to prevent undesirable modes of operation of the are from the electrode.
Indicated positions of permanent magnets and ferromagnetic parts within the electrode envelope should not be interpreted to mean that these elements are permanently fixed in position. Where advantageous for specific conditions during a portion of a melting cycle, these elements could be hydraulically or mechanically moved within the confines of the electrode envelope to provide a variable flux condition for a fixed arcing distance between electrode tip and melt.
I claim as my invention:
1. Furnace apparatus including a furnace having a wall, said furnace adapted to contain at least partially electrically conductive material to be melted, an electrode including means forming an arcing surface mounted in the furnace in a position therein substantially perpendicular to the surface of the melt, electrical circuit means connected to the electrode and to the melt for producing and sustaining an arc therebetween, the are extending substantially parallel to the longitudinal axis of the electrode, material having a high permeability mounted in the electrode near the arcing surface, and means near the wall of the furnace for setting up a magnetic field having a component in the furnace substantially parallel to the axis of the electrode and perpendicular to the surface of the melt, said high permeability material attracting lines of force of said magneticfield and causing a concentrated field at the arcing surface extending'between the arcing surface and the melt, said concentrated field focusing the are between the electrode and the melt thereby preventing flaring of the arc toward the inside wall of the furnace.
2. Furnace apparatus adapted to have a melt of at least partially electrically conductive material, comprising an electrode electric circuit means connected to the electrode and the melt for producing and sustaining an arc therebetween, means near the furnace wall for generating a magnetic field having a component extending between the melt and the electrode, means in the electrode effective without requiring energizing power for increasing the strength of the component of the magnetic field to thereby focus the are.
3. Furnace apparatus comprising means for containing a melt which is at least partially electrically conductive, an electrode disposed in predetermined spaced relationship with the melt, the electrode and the melt being adapted to be connected to terminals of opposite polarity of a source of potential to produce and sustain an are between the electrode and the melt, means disposed close to the wall of the containing means for generating a magnetic field within the containing means and adjacent at least a portion of the electrode which extends axially between the electrode and the melt, the electrode including means effective without requiring energizing power for causing at least some of the magnetic field lines to depart in a desired manner from paths which they would normally tend to follow.
4. Apparatus according to claim 3 in which the electrode has means forming an arcing surface and in which the means for causing at least some of the magnetic field lines to depart from their normal paths is utilized for controlling the percentage of the total area of the arcing surface upon which said are impinges.
5. Apparatus according to claim 3 in which the electrode includes means forming an arcing surface and in which the means within the electrode for causing at least some of the magnetic field lines to depart from their normal paths is utilized to concentrate magnetic field lines in such a manner that an increased number enter or pass through said arcing surface than would so do were said latter means not present in said electrode.
6. Furnace apparatus comprising means for containing a melt which is at least partially electrically conductive, an electrode disposed in predetermined spaced relationship with the melt, the electrode and the melt being adapted to be connected to terminals of opposite polarity of a source of potential to produce and sustain an are between the electrode and the melt, means disposed close to the wall of the containing means for generating a magnetic field within the containing means and adjacent at least a portion of the electrode which extends axially between the electrode and the melt, the electrode including means effective without requiring energizing power for causing at least some of the magnetic field lines to depart in a desired manner from paths which they would normally tend to follow, the electrode being additionally characterized as having a tip forming an arcing surface, the tip being generally annular in a horizontal plane and generally U-shaped in vertical plane cross section along any radius with a space therein extending around the entire tip, said means for causing at least some of the magnetic field lines to depart from their normal paths disposed within the space and composed of high permeability material.
7. Furnace apparatus comprising means for containing a melt which is at least partially electrically conductivc, an electrode disposed in predetermined spaced relationship with the melt, the electrode and the melt being adapted to be connected to terminals of opposite polarity of a source of potential to produce and sustain an are between the electrode and the melt, means disposed close to the wall of the containing means for generating a magnetic field within the containing means and adjacent at least a portion of the electrode which extends axially between the electrode and the melt, the electrode including means effective without requiring energizing power for causing at least some of the magnetic field lines to depart in a desired manner from paths which they would normally tend to follow, the electrode being additionally characterized as including a supporting column with a tip, the supporting column including means forming a generally cylindrical space of at least a predetermined width, and the means for causing at least some of the magnetic field lines to depart from their normal paths is generally annular and disposed within the space and composed of high permeability material.
8. Furnace apparatus comprising means for containing a melt which is at least partially electrically conductive, an electrode disposed in predetermined spaced re-- lationship with the melt, the electrode and the melt being adapted to be connected to terminals of opposite polarity of a source of potential to produce and sustain an are between the electrode and the melt, means disposed close to the wall of the containing means for generating a magnetic field within the containing means and adjacent at least a portion of the electrode which extends axially between the electrode and the melt, the electrode including means effective without requiring energizing power for causing at least some of the magnetic field lines to depart in a desired manner from paths which they would normally tend to follow, the electrode being additionally characterized as including a supporting column with a tip, the tip having a space therein extending around the tip, the column having means fonning a generally cylindrical space of at least a predetermined width, the space in the tip being radially aligned with the space in the column, the spaces opening into each other, the means for causing at least some of the magnetic field lines to depart from their normal paths being generally annular and composed of high permeability material occupying at least one of the spaces within the column and the tip.
9. Apparatus according to claim 8 in which the high permeability material occupies both the space within the tip and at least a portion of the space within the column.
l0. Furnace apparatus adapted to have a melt of at least partially electrically conductive material, comprising an electrode spaced from said melt, electric circuit means connected to the electrode and the melt for producing and sustaining an arc therebetween, at least one element for generating a magnetic field, at least one other element as part of the electrode being effective without requiring energizing power, the first and second elements cooperating with each other to produce a resultant magnetic field pattern which is shaped and dimensioned to control at least one of the operating parameters of the furnace apparatus including the total area on the electrode surface from which the arc takes place, the particular portion of the electrode surface from which the arc takes place, the total area of the surface of the melt upon which the arc impinges, the particular portion of the surface of the melt upon which the arc impinges.

Claims (10)

1. Furnace apparatus including a furnace having a wall, said furnace adapted to contain at least partially electrically conductive material to be melted, an electrode including means forming an arcing surface mounted in the furnace in a position therein substantially perpendicular to the surface of the melt, electrical circuit means connected to the electrode and to the melt for producing and sustaining an arc therebetween, the arc extending substantially parallel to the longitudinal axis of the electrode, material having a high permeability mounted in the electrode near the arcing surface, and means near the wall of the furnace for setting up a magnetic field having a component in the furnace substantially parallel to the axis of the electrode and perpendicular to the surface of the melt, said high permeability material attracting lines of force of said magnetic field and causing a concentrated field at the arcing surface extending between the arcing surface and the melt, said concentrated field focusing the arc between the electrode and the melt thereby preventing flaring of the arc toward the inside wall of the furnace.
2. Furnace apparatus adapted to have a melt of at least partially electrically conductive material, comprising an electrode electric circuit means connected to the electrode and the melt for producing and sustaining an arc therebetween, means near the furnace wall for generating a magnetic field having a component extending between the melt and the electrode, means in the electrode effective without requiring energizing power for increasing the strength of the component of the magnetic field to thereby focus the arc.
3. Furnace apparatus comprising means for containing a melt which is at least partially electrically conductive, an electrode disposed in predetermined spaced relationship with the melt, the electrode and the melt being adapted to be connected to terminals of opposite polarity of a source of potential to produce and sustain an arc between the electrode and the melt, means disposed close to the wall of the containing means for generating a magnetic field within the containing means and adjacent at least a portion of the electrode which extends axially between the electrode and the melt, the electrode including means effective without requiring energizing power for causing at least some of the magnetic field lines to depart in a desired manner from paths which they would normally tend to follow.
4. Apparatus according to claim 3 in which the electrode has means forming an arcing surface and in which the means for causing at least some of the magnetic field lines to depart from their normal paths is utilized for controlling the percentage of the total area of the arcing surface upon which said arc impinges.
5. Apparatus according to claim 3 in which the electrode includes means forming an arcing surface and in which the means within the electrode for causing at least some of the magnetic field lines to depart from their normal paths is utilized to concentrate magnetic field lines in such a manner that an increased number enter or pass through said arcing surface than would so do were said latter means not present in said electrode.
6. Furnace apparatus comprising means for containing a melt which is at least partially electrically conductive, an electrode disposed in predetermined spaced relationship with the melt, the electrode and the melt being adapted to be connected to terminals of opposite polarity of a source of potential to produce and sustain an arc between the electrode and the melt, means disposed close to the wall of the containing means for generating a magnetic field within the containing means and adjacent at least a portion of the electrode which extends axially between the electrode and the melt, the electrode including means effective without requiring energizing power for causing at least some of the magnetic field lines to depart in a desired manner from paths which they would normally tend to follow, the electrode being additionally characterized as having a tip forming an arcing surface, the tip being generally annular in a horizontal plane and generally U-shaped in vertical plane cross section along any radius with a space therein extending around the entire tip, said means for causing at least some of the magnetic field lines to depart from their normal paths disposed within the space and composed of high permeability material.
7. Furnace apparatus comprising means for containing a melt which is at least partially electrically conductive, an electrode disposed in predetermined spaced relationship with the melt, the electrode and the melt being adapted to be connected to terminals of opposite polarity of a source of potential to produce and sustain an arc between the electrode and the melt, means disposed close to the wall of the containing means for generating a magnetic field within the containing means and adjacent at least a portion of the electrode which extends axially between the electrode and the melt, the electrode including means effective without requiring energizing power for causing at least some of the magnetic field lines to depart in a desired manner from paths which they would normally tend to follow, the electrode being additionally characterized as including a supporting column with a tip, the supporting column including means forming a generally cylindrical space of at least a predetermined width, and the means for causing at least some of the magnetic field lines to depart from their normal paths is generally annular and disposed within the space and composed of high permeability material.
8. Furnace apparatus comprising means for containing a melt which is at least partially electrically conductive, an electrode disposed in predetermined spaced relationship with the melt, the electrode and the melt being adapted to be connected to terminals of opposite polarity of a source of potential to produce and sustain an arc between the electrode and the melt, means disposed close to the wall of the containing means for generating a magnetic field within the containing means and adjacent at least a portion of the electrode which exteNds axially between the electrode and the melt, the electrode including means effective without requiring energizing power for causing at least some of the magnetic field lines to depart in a desired manner from paths which they would normally tend to follow, the electrode being additionally characterized as including a supporting column with a tip, the tip having a space therein extending around the tip, the column having means forming a generally cylindrical space of at least a predetermined width, the space in the tip being radially aligned with the space in the column, the spaces opening into each other, the means for causing at least some of the magnetic field lines to depart from their normal paths being generally annular and composed of high permeability material occupying at least one of the spaces within the column and the tip.
9. Apparatus according to claim 8 in which the high permeability material occupies both the space within the tip and at least a portion of the space within the column.
10. Furnace apparatus adapted to have a melt of at least partially electrically conductive material, comprising an electrode spaced from said melt, electric circuit means connected to the electrode and the melt for producing and sustaining an arc therebetween, at least one element for generating a magnetic field, at least one other element as part of the electrode being effective without requiring energizing power, the first and second elements cooperating with each other to produce a resultant magnetic field pattern which is shaped and dimensioned to control at least one of the operating parameters of the furnace apparatus including the total area on the electrode surface from which the arc takes place, the particular portion of the electrode surface from which the arc takes place, the total area of the surface of the melt upon which the arc impinges, the particular portion of the surface of the melt upon which the arc impinges.
US00291470A 1972-09-22 1972-09-22 Electric arc furnace apparatus having a shaped magnetic field for increasing the utilized area of the arcing surface of an electrode and improving the heating efficiency Expired - Lifetime US3783170A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4495625A (en) * 1983-07-05 1985-01-22 Westinghouse Electric Corp. Magnetic field stabilized transferred arc furnace
US5939012A (en) * 1997-12-12 1999-08-17 Globe Metallurgical, Inc. Method and apparatus for manufacture of carbonaceous articles

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3610796A (en) * 1970-01-21 1971-10-05 Westinghouse Electric Corp Fluid-cooled electrodes having permanent magnets to drive the arc therefrom and arc heater apparatus employing the same
US3683094A (en) * 1971-02-18 1972-08-08 Max P Schlienger Arc positioning system for rotating electrode wheel arc furnace

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3610796A (en) * 1970-01-21 1971-10-05 Westinghouse Electric Corp Fluid-cooled electrodes having permanent magnets to drive the arc therefrom and arc heater apparatus employing the same
US3683094A (en) * 1971-02-18 1972-08-08 Max P Schlienger Arc positioning system for rotating electrode wheel arc furnace

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4495625A (en) * 1983-07-05 1985-01-22 Westinghouse Electric Corp. Magnetic field stabilized transferred arc furnace
US5939012A (en) * 1997-12-12 1999-08-17 Globe Metallurgical, Inc. Method and apparatus for manufacture of carbonaceous articles

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